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Pouring A Concrete Slab

Every builder has a story about forms that collapsed or bulged due to force of the concrete, to avoid your own horror story you must build strong forms. Depending on the thickness of the concrete 4 inches or 6 inches choosing the right material can make all the difference. There are a few things to know before you build and pour a concrete slab or walkway. First of all you must start with a solid base be sure to excavate a few inches below the thickness of the slab. For instance if your pouring a 4 inch slab or walkway a 2×4 is 3 ½ inches wide so you will then need to remove a total of 5 ½ inches to 6 ½ inches of material depending on overall finished height of landscape, So the 5 ½ inches minus 2 inches equals 3 ½ inches, a solid base of 2 inches is key. Material used for the base should consist of ¾ minus which is the typical aggregate used as it interlocks when wet and compacted it’s also easy to work with and less expensive to use. Shale is another good choice but mostly used when building or pouring larger areas of concrete, tends to be a base for ¾ minus. (Never pour concrete on dirt). Now you have a solid base to work on next is reinforcement.

Reinforcement

This can be done a few different ways either with rebar or welded wire mesh; the purpose of reinforcement is to minimize cracking. Whether you decide to use 2×4 material or a bender board for forms make sure stakes wood/steel are placed close enough together so when the concrete is placed it does not collapse. When building forms over 6 inches kicker boards may be necessary kicker boards are simply braces to secure forms in place and are braced to another stake 12 to 16 inches away this ensures that forms stay firm and in place. Be sure to keep stakes out of the way either hammer all the way down or as far as they will go then cut them off flush with form material.

Concrete

Depending on the size of the slab or walkway you may need to consider ordering concrete and having it delivered, there are a few options here such as having the concrete truck place the concrete in a wheelbarrow although you’ll have to make several trips this method is used for smaller jobs. Another method is hiring a concrete pump company, what this does is allow the concrete to get from the truck to the desired location most of the time the concrete truck can’t get to the desired location that’s where the pump comes in. When ordering concrete ask them to set up a pump to go with the truck this is also a preferred method this way you only need to make one call. Keep in mind concrete companies have a minimum usually 2 yards and additional fees may apply, there are concrete companies that will mix in a lessor amount called a short load meaning 1 yard and under. So mixing from the sack may be your only option if the volume is small either in a wheelbarrow or by renting a cement mixer.

Avoid Too Much Water

Most of the time when the concrete truck shows up the consistency of the mix is right. Extra water weakens the mix not to mention it takes longer for the concrete to dry, if your mixing your own from the sack be careful not to add to much water, you want the mix to be chunky sort of like chunky peanut butter. What happens when you float the concrete the water comes to the surface usually when pouring concrete slabs or walkways the mix is never too dry but too wet, you can always add water to a dry mix, unless you have sacks of concrete laying around go easy on the water it will makes for a much nicer looking finish.

Screed Board

A screed board is used to set a rough height, its best to use a screed board in a sawing motion this makes moving the concrete easier. If concrete is being delivered have an empty 5 gallon bucket or maybe two just in case you have a larger pour place some concrete in them to make sure you have a little extra after the truck leaves. There may not always be enough time to screed while concrete is being pumped that is why the 5 gallon buckets come in handy for this reason. Float as you screed if you get a chance to try not to leave floating till the end especially on hotter days this could result in a disaster float the concrete until the cream comes to the surface. Depending on the size of your project you may need a bull float otherwise a mag float is acceptable for smaller projects like walkways, and patios. It’s best to have a helper on bigger projects so one can screed and the other can use the float, since hotter days can prove to test your ability and skill level. If you notice too much water when floating stop for a while until water evaporates some then proceed to finish.

Control Joints

Those grooves in the concrete have a purpose, control joints minimize cracking they also limit cracks that may form later. The idea here is that if the concrete has the chance to crack it will crack along the control joint. There are a couple of ways to make a control joint by either using a groove tool or cut them in after the concrete has cured for a day or two. Concrete cut saws are available to rent by the half day or full day. Control joints should be no more than 5ft on sidewalks and 7ft on driveways and slabs. If you plan to cut the control joints with a concrete saw snap all the lines first then using a clear spray paint over the chalk lines doing this will ensure the lines stays when water is applied during cutting. Depth of control joint should be ¼ the thickness of the slab. Always use a straight edge with a groove tool this will ensure straight lines you can also use a 2×4 as a guide.

Finish Trowel

This is the final process before brooming and the most difficult, as it takes patience and skill one thing to remember is not to trowel too much or the sand comes to the top, in this step all you want to do is put a smooth even finish on the concrete. Don’t be too worried about fine lines from the trowel these will disappear when brooming.

Add Texture with a Broom

Unless you’re wanting the smooth look of concrete a finish trowel leaves a slippery surface when wet or icy. Depending on the location of the new concrete a broom may be a great choice, it also adds a nice look and will not show imperfections, dragging a broom across the surface will give a non-slip surface. Weather conditions vary from time of finish trowel to brooming; you want it to be dry enough to leave a good texture and lines you can always try by using the broom in a corner or even and old paint brush if you’re unsure. Also let the weight of the broom do the work unless you want a more aggressive look or even a certain pattern make sure to overlap brush strokes by a few inches be sure to go slow and get brush lines nice and straight. Brooms can be purchased from home centers or specialized retailers or you can even use an old shop broom.

Slow the Curing

Depending on the weather it may be necessary to cover the concrete with 6 mil plastic, or apply a concrete cure both of these methods work well for slowing down the cure time. Appling 6 mil plastic works well if a pour must be done in lower temperatures, or if it rains. If you choose to use the cure you can do so by using a garden pump sprayer to apply. If and when pouring concrete is a must in lower temperatures such as below freezing (concrete blankets) are a must, although if these are not available another option is to lay down some 6 mil plastic or if the concrete is dry to touch then you can apply straw right on the concrete if not lay down plastic first, the straw acts as an insulation. Water in the concrete can freeze causing the top to pop. Make sure to use plenty of straw to make it thick.Avoiding concrete mistakes can save time and money.

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